This application claims the priority of German patent 198 28 835.2-25, filed Jun. 27, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a tension rod for use as a chord for bridges, having a middle part made of fiber composite and having ends made of metal material.
Fiber composites exhibit high stiffness and strength relative to their specific density. This property makes them especially valuable for lightweight construction applications. Advantages are realized especially when the fibers can be subjected to tensile stress in the lengthwise direction.
Structural elements of this kind are subjected primarily to locally concentrated forces which often also have different directions in space.
When a part stressed in this fashion is developed using fiber construction, the introduction of forces into the fibers poses a problem which as a rule must be solved at high cost. These costly solutions are accordingly expensive so that they are rarely chosen for applications outside of aviation and space travel. In addition, many of the advantages of fiber materials are lost in multiaxially stressed states.
For example, winding techniques are used in which the fibers are wound at the end around a metal eye. This is a very expensive method for manufacturing, quality assurance, and monitoring of service life.
Methods are also known in which the ends of the fibers are clamped in a cone that is subjected to tensile force.
In addition, glued tapered overlaps between the fiber composite and metal fittings are also known for simple requirements but these, in the case of primary components and high loads, are additionally secured by bolts or rivets in order to be able to accept the load if the glued connection fails.
Very strict requirements are imposed on mobile bridges regarding weight, dimensions, rigidity, and strength so that the use of fiber composite materials is attractive. However, there are the following problems with using fiber composite materials:
(a) Relatively high sensitivity to mechanical damage.
(b) Mobile bridges must be taken apart into transportable units. This means that high concentrated forces must be repeatedly introduced into and brought out from the structures.
(c) A bridge structure, for practical and economic reasons, can be examined for damage only at relatively long intervals, in other words the structure must be reliable, error-tolerant, and easy to check.
An object goal of the invention is to provide a tension rod made of fiber composite material for use as a chord for mobile bridges. This and other objects have been achieved according to the present invention by providing a tension rod for use as a chord for bridges, comprising at least one chord including: a middle part made of a fiber composite material; and a pair of end parts made of a metallic material, wherein each of said end parts is connected to said middle part via a glued tapered overlap, the middle part and the end parts having rectangular cross sections at said overlap, a length of said overlap being greater than a thickness of the tension rod at the overlap, and said overlap of the fiber composite part and the metal part extending bladewise on the thin sides.
This and other objects have been achieved according to the present invention by providing a tension rod, comprising at least one chord including: a middle part made of a fiber composite material, said middle part having a rectangular cross section which gradually decreases in thickness at each longitudinal end to define tapered connection areas; a pair of end parts made of a metallic material, each of said end parts having a rectangular cross section which gradually decreases in thickness at one longitudinal end to define a tapered connection area which matingly corresponds to the respective tapered connection area of the middle part; and a glued connection between said tapered connection areas of the middle part and said tapered connection areas of the end parts, respectively.
This and other objects have been achieved according to the present invention by providing a method of making a tension rod, comprising: providing a middle part made of a fiber composite material, said middle part having a rectangular cross section which gradually decreases in thickness at each longitudinal end to define tapered connection areas; providing a pair of end parts made of a metallic material, each of said end parts having a rectangular cross section which gradually decreases in thickness at one longitudinal end to define a tapered connection area which matingly corresponds to the respective tapered connection area of the middle part; and gluing said tapered connection areas of the middle part to said tapered connection areas of the end parts, respectively.
The subject of the invention is the introduction of forces into, or their departure from, a fiber composite by a tapered overlap designed according to the invention with the following properties:
(a) The cost is only a fraction of that for a solution involving winding.
(i) The fiber composite can be manufactured economically; manufacture can be automated.
(ii) The metal end fittings are likewise parts that are simple to manufacture.
(iii) The gluing of the parts is likewise economical because of the geometry and can be automated.
(iv) A chord consists of only two different individual parts which therefore can be manufactured in correspondingly large numbers.
(b) Having metal end fittings at the coupling points that are subjected to high mechanical loads ensures that the fiber composite is not damaged mechanically when coupling.
(c) The present invention is well-suited for repeated introduction and departure of forces without making the design extremely expensive as a result or calling into question the advantages of the fiber composite.
(d) The chords are reliable, error-tolerant, and readily checked.
(i) The reliability of the chord depends to a large degree on the quality of gluing during manufacture. By constructing the chords from individually manufactured elements with the simplest geometry, the chords can be checked 100% following each workstep using conventional methods such as ultrasound or x-rays.
(ii) The reliability of the chord also depends on a possible aging of the glue during operation by the penetration of water vapor. The design of the tapered overlap provides the highly stressed large-area glued connections of the overlap relative to the environments with excellent protection by the metal fittings against the penetration of water vapor. The very small lateral surfaces can be protected with known methods, for example by a glued metal film, 0.1 to 0.3 mm thick.
(iii) If individual elements should fail, the layer-wise construction ensures that cracks cannot propagate further.
(iv) The chords can also be checked as double or multiple chords using the same test procedures as during a manufacture.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.